Question

Two electrical bulbs have tungsten filament of same length. If one of them gives 60 watts and other 100 watts, then

• A. 100 watts bulb has thicker filament
• B. 60 watt bulb has thicker filament
• C. Both filaments are of same thickness
• D. It is impossible to get different wattage unless lengths are different

Answer 1

Answer: (A)

100 watts bulb has thicker filament

power $P=\frac{V^2}{R}$, where $V$ is the voltage and $R$ is the resistance.

So for higher power, the resistance should be less.

Therefore, the resistance of $100W$ bulb should be less.

We know that resistance $R=\frac{\rho l}{A}$, where $\rho$ is the resistivity, $l$ is the length, and $A$ is the area.

when the resistivity and the length are fixed, the area should be more for less resistance.

Thus, the $100W$ bulb should have a thicker filament.